Mysimba is a prescription weight loss medication that combines two active ingredients — naltrexone and bupropion — to help regulate appetite and reduce food cravings. While it can be a valuable part of a medically supervised weight loss programme, it’s common for new users to experience side effects as their body adjusts.
At Mendus Pharmacy, we support many patients through their Mysimba journey. One of the most frequent questions we hear is: How long do Mysimba side effects last? In this post, we’ll walk you through a general week-by-week guide so you know what to expect and when things should begin to settle.
Week 1: Getting Started – Mild and Manageable
Mysimba is introduced gradually to reduce the likelihood and severity of side effects. In the first week, you’ll typically take one tablet per day, which helps your body ease into treatment.
Common side effects in week one include:
Nausea
Headache
Dry mouth
Trouble sleeping (insomnia)
Dizziness
These side effects are usually mild and improve within a few days. Taking your dose in the morning and avoiding caffeine or alcohol can help minimise discomfort.
Week 2: Increasing the Dose – Your Body Adjusts
In week two, your dose increases to one tablet in the morning and one in the evening. This step-up may cause a slight return or increase in side effects, particularly nausea, restlessness, or disturbed sleep.
At this stage, some patients may experience:
Increased anxiety or irritability
Mild gastrointestinal discomfort
Lack of appetite (which is also part of the intended effect)
Most symptoms remain manageable, and many people notice they begin to feel less hungry or experience fewer cravings, which is a sign the medication is starting to take effect.
Week 3: Another Increase – Watch for Nausea or Dizziness
By now, you’ll likely be taking three tablets a day — two in the morning and one in the evening. This is often the peak time for Mysimba side effects, particularly nausea, dizziness, or dehydration.
If you’re struggling with these symptoms:
Take tablets with food, even a small snack
Drink plenty of water to stay hydrated
Take your evening dose earlier, to reduce impact on sleep
Most patients find the side effects subside gradually after this adjustment period, but everyone reacts differently.
Week 4: Reaching the Full Dose – Symptoms Begin to Stabilise
In week four, the target maintenance dose is reached: two tablets in the morning and two in the evening (a total of four per day). While some people continue to experience low-level side effects, this is typically when your body starts to settle.
By this stage, common side effects may include:
Occasional dizziness or headache
Mild constipation or stomach upset
Dry mouth or metallic taste
Improved appetite control
If side effects persist or worsen at this point, it’s important to speak to your prescribing pharmacist or GP. In rare cases, adjustments to your dose or stopping the medication may be recommended.
Weeks 5–8: Settling In – Fewer Side Effects, More Benefits
From the fifth week onward, most patients report significant improvement in side effects. Your body has likely adapted to the active ingredients, and any lingering symptoms tend to fade completely.
This is often when the benefits become more noticeable, including:
Less frequent hunger and snacking
Better control over cravings and portion sizes
Gradual weight loss when combined with healthy eating and movement
You should continue regular check-ins with your healthcare provider to monitor your progress, weight, and any remaining side effects.
When to Seek Advice
While most Mysimba side effects are mild and temporary, some symptoms require medical attention. Contact your pharmacist or GP if you experience:
Severe or persistent nausea or vomiting
Heart palpitations or chest pain
Severe anxiety, low mood, or thoughts of self-harm
Seizures or fainting episodes
Sudden allergic reactions such as swelling or difficulty breathing
Your safety is our top priority, and we’re here to help you adjust your treatment plan if needed.
Support Through Every Stage at Mendus Pharmacy
At Mendus Pharmacy, we offer a full private weight loss support service, including:
One-to-one consultations
Mysimba prescription and dispensing
Side effect management guidance
Regular progress reviews and motivation support
Starting any new medication can feel daunting, but with the right support and information, you can stay on track towards your health goals.
If you’re considering Mysimba or want help managing side effects, contact us today to speak to one of our trained pharmacists. We’re here to guide you every step of the way.