Prolax is fluoxetine 20 mg, an antidepressant of the SSRI class. It is prescribed for depression, obsessive-compulsive disorder, bulimia nervosa and panic disorder. It takes weeks to work, which is the single most important thing to know before starting it.
What is Prolax?
Prolax contains fluoxetine 20 mg. The South African Medicine Price Registry lists it as a Schedule 5 capsule.
Fluoxetine is a selective serotonin reuptake inhibitor (SSRI). Nerve cells communicate using chemical messengers, and after a message is sent the messenger is normally reabsorbed. Fluoxetine blocks the reabsorption of serotonin, so more of it remains available in the synapse.
That is the mechanism, but it is not the full explanation. The reuptake block happens within hours, while the clinical benefit takes weeks — so the improvement almost certainly comes from slower downstream changes in how nerve cells adapt, rather than from the serotonin increase itself.
That gap between mechanism and effect matters practically, and it is worth spelling out:
Weeks one to two: side effects appear — nausea, restlessness, disturbed sleep. Mood has not lifted. This is the phase where many people conclude the medicine is not working, or is making things worse, and stop.
Weeks two to four: sleep, appetite and energy often improve before mood does.
Weeks four to six: mood typically begins to lift. Full benefit may take eight to twelve weeks.
Fluoxetine is also the longest-acting SSRI by a wide margin — it and its active metabolite persist for weeks. That has two consequences: missing a dose matters less than with other antidepressants, and withdrawal symptoms on stopping are usually milder. It also means it takes weeks to clear if a switch is needed.
What is Prolax commonly used for?
- Depression — moderate to severe, and persistent milder depression.
- Obsessive-compulsive disorder (OCD), often at higher doses and over longer periods.
- Bulimia nervosa — fluoxetine is the best-evidenced medicine for it, usually at a higher dose than for depression.
- Panic disorder, with or without agoraphobia.
- Premenstrual dysphoric disorder (PMDD), sometimes taken only in the second half of the cycle.
- Anxiety disorders, including social anxiety and generalised anxiety.
- Depression in children and adolescents, where fluoxetine is the SSRI with the most supportive evidence — under specialist supervision.
Three points shape how well treatment goes.
It is not a happy pill and not a sedative. It does not blunt normal emotion or produce a lift on a bad day. It treats a condition.
It works better alongside therapy than alone, for most people and most conditions on that list.
Do not stop when you feel better. Treatment normally continues for at least six months after recovery, and longer after repeated episodes. Stopping early is one of the most reliable predictors of relapse.
How Prolax fits into this medicine category
| Group | Examples | Where it fits |
|---|---|---|
| SSRIs | Fluoxetine (Prolax), escitalopram, sertraline, citalopram | First-line for depression and most anxiety disorders |
| SNRIs | Venlafaxine, duloxetine | Depression, anxiety, some nerve pain |
| Tricyclics | Amitriptyline (Trepiline) | Depression, nerve pain; more side effects |
| Mood stabilisers | Lithium, valproate, carbamazepine | Bipolar disorder |
| Benzodiazepines | Oxazepam, lorazepam | Short-term severe anxiety; dependence risk |
| Sleep agents | Zolpidem and related medicines | Short-term insomnia |
SSRIs differ mainly in side effects, interactions and duration rather than in how well they work. Fluoxetine’s long duration is its distinguishing feature. See the mental health and neurology medicines hub.
What to check before using Prolax
Tell your doctor if you have ever had a manic episode, or been diagnosed with bipolar disorder. An antidepressant given alone in bipolar disorder can trigger mania. This is one of the most important questions before starting any antidepressant, and it is easily missed if nobody asks.
Also tell your doctor or pharmacist if you:
- Take tramadol, triptans for migraine, lithium, other antidepressants, or St John’s wort. These raise the risk of serotonin syndrome in combination.
- Have taken an MAOI antidepressant in the past two weeks — this combination is dangerous, and because fluoxetine lasts so long, a five-week gap is needed the other way round.
- Take warfarin, aspirin or anti-inflammatories. SSRIs affect platelets and the combination raises bleeding risk.
- Take tamoxifen — fluoxetine can reduce its effectiveness.
- Have epilepsy, liver disease, diabetes, glaucoma, or a heart rhythm problem.
- Have a history of bleeding disorders.
- Are pregnant, planning pregnancy or breastfeeding. Untreated depression in pregnancy carries its own risks, so this is a discussion rather than an automatic stop.
- Are under 25. There is a small increased risk of suicidal thoughts early in treatment in young people, which is why close monitoring in the first weeks matters.
Practical points:
- Take it in the morning, as it can disturb sleep.
- Take it consistently, with or without food.
- Do not stop abruptly without advice — though withdrawal is milder with fluoxetine than most SSRIs.
- Avoid alcohol, at least early on.
- Do not drive until you know how it affects you.
- Make sure someone knows you have started, and can tell you if they notice changes you do not.
Possible cautions and when to ask a pharmacist or doctor
Common early effects are nausea, headache, difficulty sleeping, restlessness or agitation, reduced appetite, dry mouth, sweating and diarrhoea. Most settle within one to two weeks.
Sexual side effects — reduced desire, delayed orgasm, erectile difficulty — are common, often persist, and are frequently not mentioned by either side. They are a legitimate reason to change treatment, and worth raising rather than enduring or quietly stopping.
Get emergency help for:
- Serotonin syndrome — agitation, confusion, fever, sweating, shivering, muscle twitching, a racing heart. More likely when another serotonergic medicine has been added.
- Thoughts of harming yourself, or a sudden worsening of mood. This is most likely in the first weeks and in younger people. Tell someone immediately and seek help the same day.
- A manic episode — unusually elevated mood, racing thoughts, greatly reduced need for sleep, risky behaviour.
- Seizures.
- Unusual bruising or bleeding, black stools, or vomiting blood.
- Swelling of the face, lips or tongue, difficulty breathing, or a blistering rash.
Contact your doctor if there is no improvement after four to six weeks at a proper dose, if side effects are not settling, if you are thinking of stopping, or if you feel worse rather than better. There are many antidepressants, and a poor response to one does not predict a poor response to another — but that conversation has to happen with a prescriber rather than by stopping quietly.
Related medicine guides
Frequently asked questions
What are Prolax capsules used for? Depression, obsessive-compulsive disorder, bulimia nervosa, panic disorder and some anxiety disorders. It contains fluoxetine 20 mg.
How long before it works? Sleep, appetite and energy often improve in two to four weeks; mood typically lifts by four to six, with full benefit taking up to twelve.
Is it addictive? No. It does not cause craving or dependence. Stopping abruptly can cause withdrawal symptoms, though these are milder with fluoxetine than most SSRIs.
Can I stop when I feel better? No. Treatment usually continues at least six months after recovery. Stopping early is a leading cause of relapse.
Will it change my personality? No. It treats the condition; it does not blunt normal emotion or create artificial happiness.
Can I drink alcohol on it? Best avoided, particularly early on. Alcohol worsens depression and adds to drowsiness.
Why must I take it in the morning? Fluoxetine can be activating and disturb sleep if taken later in the day.
Can I take it with tramadol or migraine medicine? Tell your doctor. Combining serotonergic medicines raises the risk of serotonin syndrome.