Side effects of weight loss medication

Carrying excess weight can affect your health and the way you feel about yourself and your body. Diet and exercise are a tried and tested formula for losing weight. However, for many people, their weight or health problems can make losing weight this way particularly difficult, and so forming healthy habits can be a struggle. Fortunately, there are other options to consider, including weight loss treatments.

Understandably, some people may have concerns about whether weight loss treatments are safe, if they will experience any side effects when using them and what these are likely to be. Here, we’ll take a look at some of the safest weight loss treatments and break down what you should know before you start using them.

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Medically reviewed by

Dr Daniel Atkinson

Clinical Reviewer

on Nov 07, 2024.

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Last updated on Nov 07, 2024.

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Side effects of weight loss treatments

First of all, it’s important to know that using a treatment isn’t a shortcut to weight loss. Those who choose to take them will still need to commit to making healthy food choices and taking part in regular physical activity. It’s also important to be aware that all medications, no matter what they’re treating, have the potential to cause side effects. Since everybody is different, which side effects (if any) you may experience and how severe they can be will vary.

Some of the most common side effects associated with taking weight loss treatments include:

Nausea
Constipation or diarrhea
Vomiting
Headaches
Insomnia
Dry mouth

Before commencing a course of any medication it’s a good idea to familiarize yourself with the potential side effects by reading the patient information leaflet.

Orlistat side effects

Orlistat is one of the most well-known weight loss drugs, and is the generic name for Xenical. Orlistat is also the name of the active ingredient in Xenical, and several other weight loss medications.

Orlistat works by altering the way that fat is absorbed by the body, preventing around a third of the fat from the food you eat being absorbed. Instead, it is passed out through your digestive system when you empty your bowels. This means that while it is effective in preventing you from gaining weight, you won’t necessarily lose weight unless you also follow a calorie-deficit diet and take regular exercise. A clinical study showed that after a year, patients who took orlistat lost significantly more weight than those who took a placebo.

But is Orlistat safe? Orlistat is considered to be extremely safe and can be a suitable weight loss aid for those within the outlined BMI perimeters. A doctor should assess whether it’s suitable for you when it’s prescribed at a 120mg dosage.

Very common Orlistat side effects
Common Orlistat side effects
Unknown frequency Orlistat side effects

(affects 1 to 10 users out of 100)

Headache
Abdominal pain/discomfort
Oily discharge
Oily or fatty stools
Liquid stools
Urgent or increased need to open the bowels
Flatulence with discharge
Low blood sugar levels (experienced by some people with type 2 diabetes).

(affects 1 to 10 users out of 100)

Rectal pain or discomfort
Tooth or gum disorder
Irregular menstrual cycle
Tiredness
Soft stools
Incontinence (stools)
Bloating (experienced by some people with type 2 diabetes).

Allergic reactions - with symptoms such as itching, rash, wheals, severe difficulty in breathing, nausea, vomiting and feeling unwell
Skin blistering
Diverticulitis
Bleeding from the rectum
Increases in the levels of some liver enzymes may be found in blood tests.
Hepatitis (inflammation of the liver) - with symptoms such as yellowing skin and eyes, itching, dark coloured urine, stomach pain and liver tenderness (sometimes with loss of appetite). Stop taking orlistat and inform your doctor.
Gallstones.
Pancreatitis (inflammation of the pancreas).
Oxalate nephropathy (build up of calcium oxalate which may lead to kidney stones).
Vitamin deficiency - some fatty foods can be rich in certain vitamins therefore reducing fat in the diet or not absorbing fats can lead to deficiencies. This can be checked on by having a blood test to look at vitamin levels a couple of times a year.]

Xenical side effects

Xenical is a prescription brand weight loss drug; the active ingredient is Orlistat. This means that this medication works in exactly the same way and the side effects that you could experience remain the same.

Very common Xenical side effects
Common Xenical side effects
Unknown frequency Xenical side effects

(affects more than 1 in 10 users)

Headache
Abdominal pain/discomfort
Oily discharge
Oily or fatty stools
Liquid stools
Urgent or increased need to open the bowels
Flatulence with discharge
Low blood sugar levels (experienced by some people with type 2 diabetes).

(affects more than 1 in 10 users)

Rectal pain or discomfort
Tooth or gum disorder
Irregular menstrual cycle
Tiredness
Soft stools
Incontinence (stools)
Bloating (experienced by some people with type 2 diabetes).

Allergic reactions - with symptoms such as itching, rash, wheals, severe difficulty in breathing, nausea, vomiting and feeling unwell
Skin blistering
Diverticulitis
Bleeding from the rectum
Increases in the levels of some liver enzymes may be found in blood tests.
Hepatitis (inflammation of the liver) - with symptoms such as yellowing skin and eyes, itching, dark coloured urine, stomach pain and liver tenderness (sometimes with loss of appetite). Stop taking orlistat and inform your doctor.
Gallstones.
Pancreatitis (inflammation of the pancreas).
Oxalate nephropathy (build up of calcium oxalate which may lead to kidney stones).
Vitamin deficiency]

Contrave side effects

Contrave is a fairly new treatment for weight loss that works a little differently to Orlistat. Contrave targets the areas of the brain that regulate appetite, reducing food cravings and suppressing feelings of hunger. This makes it easier for patients to stick to a healthy diet and remain on a successful weight loss program. It is only available by prescription and contains active ingredients naltrexone and bupropion.

As with any other weight loss medication, there are a range of side effects associated with taking Contrave.

Very common Contrave side effects
Common Contrave side effects
Uncommon Contrave side effects
Rare Contrave side effects

(may affect more than 1 in 10 users)

Constipation
Headache
Nausea
Vomiting.

(may affect up to 1 in 10 users)

Hot flush
Increased blood pressure (sometimes severe)
Pain in the upper part of the abdomen
Pain in the abdomen
Excessive sweating (hyperhidrosis)
Rash, itching (pruritus)
Hair loss (alopecia)
Irritability
Feeling jittery
Anxiety
Dizziness (vertigo)
Feeling shaky (tremor)
Difficulty in sleeping (avoid taking Contrave near to bedtime)
Changes in the taste of food (dysgeusia) or dry mouth
Difficulty concentrating
Feeling tired and sleepy, drowsy or a lethargic
Ringing in the ears (tinnitus)
Fast or irregular heartbeat.

(may affect up to 1 in 100 users)

Hives (urticaria)
Hypersensitivity
Difficulty in getting or keeping an erection
Feeling abnormal, weakness (asthenia)
Thirst, feeling hot
Chest pain
Increased appetite and/or weight gain
Abnormal dreams
Feeling nervous, feeling spacey, tension, agitation, mood swings,
Tremor of the head or a limb which increases when trying to perform a particular function (intention tremor)
Balance disorder
Loss of memory (amnesia),
Tingling or numbness of the hands or feet
Motion sickness
Burping
Abdominal discomfort
Indigestion
Inflammation of the gallbladder (cholecystitis)
Increased creatinine levels in the blood (indicating loss of kidney function)
Increased liver enzymes and bilirubin levels, liver disorders.

(may affect up to 1 in 1000 users)

Low amount of certain white blood cells (Lymphocyte count decreased)
Decreased haematocrit (indicating loss of red blood cell volume)
Swelling of eyelids, face, lips, tongue or throat, which can cause great difficulty in breathing (angioedema)
Hernia
Toothache
Dental cavities
Pain in the lower part of the abdomen
Injury to the liver due to drug toxicity
Jaw discomfort
A disorder characterised by a sudden need to urinate (micturition urgency)
Irregular menstrual cycle, vaginal bleeding, dryness of the female vulva and vagina
Excessive loss of body water (dehydration)
Hallucinations
Fainting, feeling faint or loss of consciousness
Fits
Passage of fresh blood through the anus usually in or with stool (haematochezia)
Coldness of extremities (hands, feet).

Side effects of weight loss injections

Weight loss injections are an alternative to diet pills. There are several options to choose from, including Saxenda and Wegovy. These work using appetite suppression. Weight loss injections can help users keep a feeling of a satisfied appetite for longer by altering their feelings of hunger.

Saxenda side effects

Saxenda is one of the most popular weight loss injections. It works by regulating your appetite, which can lead to eating fewer calories and losing weight. It should be used in conjunction with a low calorie diet and regular exercise.

But is Saxenda safe? It has received approval to be used as a weight loss aid but like all other weight loss drugs, it can cause side effects.

Very common Saxenda side effects
Common Saxenda side effects
Uncommon Saxenda side effects
Rare Saxenda side effects
What are the side effects of stopping Saxenda?

(may affect more than 1 in 10 users)

Diarrhea,
Constipation
Feeling sick
Vomiting

(may affect more than 1 in 10 users)

Bruising, pain or irritation and the injection site
Stomach problems such as indigestion, pain, heartburn, feeling bloated, wind, burping and a dry mouth
Feeling lethargic
Change in the sense of taste
Feeling dizzy
Insomnia
Gallstones
Low blood sugar (hypoglycaemia)
Increase of pancreatic enzymes, such as lipase and amylase

(may affect up to 1 in 100 users)

Feeling generally unwell
Dehydration
Delay in the emptying of the stomach
Inflamed gallbladder
Allergic skin rash
Faster pulse

(may affect up to 1 in 1000 users)

Reduced kidney function
Acute kidney failure

Once you have achieved your weight loss goals, you’ll probably want to stop taking Saxenda and try to maintain your weight yourself. Alternatively, you may want to stop taking Saxenda if it isn’t proving as effective for you as you would like, and you would like to consider another weight loss drug.

There are no specific side effects associated with stopping Saxenda, but unless you follow a strict diet and exercise plan, you may find that you regain the weight that you have lost.

Current NICE guidance recommends limiting treatment to two years, however, there is an acknowledgement that continuing treatment beyond this can be useful for many patients who find that doing so helps maintain weight loss. Once weight loss goals are achieved, the dosage can be reduced to maintain weight.

What are the side effects of stopping Saxenda?

Once you have achieved your weight loss goals, you’ll probably want to stop taking Saxenda and try to maintain your weight yourself. Alternatively, you may want to stop taking Saxenda if it isn’t proving as effective for you as you’d like, and you want to try another weight loss drug.

There are no specific side effects associated with stopping Saxenda, but unless you follow a strict diet and exercise plan, you may find that you regain the weight that you have lost.

Are there any safe weight loss drugs?

The weight loss drugs listed above have all undergone extensive clinical trials to prove their safety and efficacy.

Taking unlicensed weight loss medications can have serious consequences for your health, as they may contain inactive or even dangerous ingredients.

To guarantee taking safe weight loss pills, consult with your doctor first. They will assess your suitability for weight loss drugs and recommend safe weight loss tablets or injections based on your individual needs.

When not to take weight loss drugs

Not everyone who is overweight or obese is automatically a suitable candidate to take weight loss drugs. For this reason, patients should consult with their doctor before starting any new medication, including those used for weight loss. They will ensure that the benefits of taking weight loss medication will outweigh the risks associated with the treatment.

Typically, patients who are not good candidates for weight loss drugs are those who are pregnant or nursing, under the age of 18 and have a BMI of less than 27.

Depending on the exact weight loss drug you choose, there may also be further factors to consider. For example, Orlistat is not recommended for patients who have conditions where food isn’t absorbed properly, or those taking certain medications like ciclosporin or warfarin. A doctor will be able to discuss medication interactions with you at your consultation.

Should I use weight loss drugs?

Choosing to use weight loss drugs to help you achieve your weight loss goals can feel like a big decision. It’s important to take the potential side effects into account.

If you want to explore the different ways you can lose weight, then it’s a good idea to explore all your options.

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