It depends on the medicine. Some work within the day, while others take weeks before you notice anything. For example, the NHS says antidepressants usually take 1 to 2 weeks to start having an effect and can take up to 8 weeks to work fully.
The best source for your medicine is the leaflet that comes with it, or your pharmacist. They can tell you what to expect and when.
Why some medicines take longer
Some medicines treat a symptom you can feel, so you notice when they start working. Others change something slowly, or treat a condition you may not feel at all. High blood pressure is one example: the CDC says most people who have it have no signs or symptoms, so feeling the same does not tell you whether the medicine is working.
Two examples from official guidance
| Medicine | What the guidance says |
|---|---|
| Antidepressants | Usually 1 to 2 weeks to start having an effect, up to 8 weeks to work fully (NHS) |
| Levothyroxine | May take several weeks before you notice a change in your symptoms (MedlinePlus) |
These are not a promise about how your own medicine will behave. Ask your pharmacist about yours.
What to do while you wait
- Keep going as prescribed, unless your doctor or pharmacist tells you otherwise. MedlinePlus says to continue levothyroxine even if you feel well, and not to stop without talking to your doctor. Some medicines need to be reduced slowly rather than stopped.
- Write down what you notice. A short note on how you feel makes the next appointment more useful. See what to record in a medication tracker.
- Do not double up to speed it along. Taking more than prescribed does not make it safer or more certain. Ask first.
Side effects can come first
The NHS says many antidepressant side effects may ease after a couple of weeks as your body gets used to the medicine. So you may notice side effects before you notice the benefit. Tell your doctor or pharmacist if they worry you, and get urgent help for anything severe.
When to ask
Ask your doctor or pharmacist if:
- you have reached the time you were told to expect a change and nothing is different
- you feel worse
- you are thinking of stopping
- you have been missing doses, because that changes what your doctor can tell from how you feel
If remembering is the hard part, these habits can help.
Frequently asked questions
Why do I feel no different after a few days?
Some medicines take weeks to have an effect, and some treat conditions you cannot feel. Ask your pharmacist what to expect from yours.
Can I stop if it isn't working?
Talk to your doctor first. Some medicines cause problems if stopped suddenly, and your doctor can tell you the safe way forward.
Does missing doses change how long it takes?
It can make it harder to judge whether a medicine is working. Tell your doctor if you have missed doses, so they have the full picture.
Sources
Antidepressants, NHS. Levothyroxine, MedlinePlus. About high blood pressure, CDC.
Cadence is a free medication reminder app for iPhone and Apple Watch. It is not medical software and does not give medical advice. Cadence Pro is a one-time purchase, with no subscription.
