The short version
- Feeling better after three days means the weakest bacteria are gone, not all of them.
- Stopping early leaves the toughest bacteria behind, so the infection often returns worse.
- It also drives antibiotic resistance, which affects everybody, not only you.
- Space doses evenly, follow the food instruction, and finish the packet.
- Stop and ask us about a rash, swelling, breathing difficulty or severe diarrhoea.
It is one of the most common things we hear across the counter: "I felt better after three days, so I stopped." It makes perfect sense. You took the medicine, the fever broke, the pain eased, and the rest of the packet went into a drawer in case it is needed again. Almost everybody has done it at some point.
The trouble is that feeling better and being better are not the same thing, and with antibiotics the gap between the two is where the problems start. This article explains what is happening inside you during a course of antibiotics, why the last few days matter as much as the first, and what to do if something goes wrong partway through.
What is happening in the first few days
An infection is a population of bacteria, and like any population it is varied. Some of those bacteria are weak and are killed within hours of your first dose. Others are naturally a little tougher and take longer. By day three, the weak majority is gone. That is why you feel better: there are far fewer bacteria producing the toxins that were making you feel ill.
What is left behind is the hardier minority. They are still there, still multiplying, just not in numbers big enough to make you feel unwell yet. The remaining days of the course exist to finish them off. Stop at that point and you have done something rather unfortunate: you have cleared away the competition and left the toughest bacteria with the whole field to themselves.
Two things can go wrong
The first is personal and immediate. The infection comes back, often within a week or two, and often worse than before, because the bacteria that survived are the ones your antibiotic struggles with. A second course is needed, sometimes a stronger one, and you are unwell for longer overall than if you had simply finished the first packet.
The second is slower and bigger than any one person. Bacteria that survive a partial course pass their resistance on, not only to their offspring but sideways to other bacteria entirely. Do that often enough across a community and the medicines that used to work stop working. That is antibiotic resistance, and it is already making some ordinary infections harder to treat than they were twenty years ago.
Talk to a pharmacist
If you are unsure whether a medicine you have been given is an antibiotic at all, bring the box in or send us a photograph of it. Not everything prescribed for an infection is one, and the advice is different for each.
What a complete course actually looks like
- Take every dose — to the end of the packet, or to the end of the number of days your prescriber specified.
- Space them evenly — twice a day means roughly twelve hours apart, not both in the evening because you forgot the morning one.
- Follow the food instruction — some antibiotics are absorbed poorly with food, others upset an empty stomach. The label tells you which.
- Finish even if the symptoms are gone — especially then, in fact.
If you miss a dose, take it as soon as you remember unless it is nearly time for the next one. In that case skip it and carry on as normal. Never take two at once to catch up: a double dose does not make up for the gap and it does make side effects more likely.
When you should stop and come back to us
Finishing the course is the rule, but there are real exceptions and you should not push through them alone. Stop and speak to a pharmacist or your prescriber straight away if you develop a rash, swelling of the face, lips or tongue, difficulty breathing, severe or bloody diarrhoea, or if you simply feel dramatically worse rather than better. These are not reasons to soldier on.
Equally, if you have finished the whole course and you still feel unwell, that is not a failure on your part and it is not a reason to start another packet you have at home. It is a reason to be seen again, because it may not be the infection anyone assumed it was.
The leftovers in the drawer
If you have part-used packets at home from previous illnesses, please do not keep them for next time and please do not share them with family. The medicine that suited one infection may do nothing for another, the dose may be wrong for a different person, and a partial packet is a partial course by definition. Bring them to us instead and we will dispose of them properly.
The same goes for antibiotics bought for a cold or flu. Those are caused by viruses, and antibiotics do nothing at all to a virus. They will not shorten the illness, they will not stop it spreading, and they will expose the harmless bacteria you carry to a medicine they can learn from. A pharmacist can suggest something that will genuinely help you feel better while the virus runs its course.
For colds and flu, something that actually helps
Decongestants, soothing syrups, lozenges and simple pain relief will not shorten a viral illness, but they will make the week far more bearable.
A short checklist for the next time you are given antibiotics
- Ask what the antibiotic is for, and how many days the course is.
- Ask whether to take it with food, and whether to avoid anything while on it.
- Tell the pharmacist about every other medicine, supplement and herbal remedy you take.
- Say if you are pregnant, breastfeeding, or have ever reacted badly to an antibiotic before.
- Set a reminder on your phone for each dose. It is the single most effective thing you can do.
Message us on WhatsApp
Halfway through a course and something does not feel right? Message us. It is quicker than waiting and worrying, and we would far rather hear from you early.
Before you leave the pharmacy
- Ask what the antibiotic is for and exactly how many days the course runs.
- Ask whether to take it with food, and what to avoid while on it.
- Tell us every other medicine, supplement and herbal remedy you take.
- Say if you are pregnant, breastfeeding, or have reacted to an antibiotic before.
- Set a phone alarm for each dose before you put the packet away.
Questions we are asked about this
Can I drink alcohol while taking antibiotics?
With most antibiotics a small amount will not stop the medicine working, but alcohol does make you more dehydrated and more tired while your body is fighting an infection, so it is better left alone. With a few antibiotics the combination causes severe flushing, vomiting and a racing heart, and those must be avoided completely. Ask us which one you have rather than assuming.
Should I take a probiotic alongside?
Some people find it reduces the stomach upset that antibiotics can cause, and the evidence is reasonable for certain situations. If you do take one, separate it from the antibiotic dose by a couple of hours. It is a sensible addition rather than an essential one, and it is not a reason to delay starting the antibiotic.
Why was I not given antibiotics for my chest infection?
Because most chest infections, like most sore throats and most ear infections, are caused by viruses and get better on their own. A clinician who decides against antibiotics has usually made a considered judgement rather than an economy. If you get worse rather than better over the following days, go back and be reassessed.
I have antibiotics left from last time. Can I use them now?
No. The medicine that suited one infection may do nothing for another, a part packet is a part course by definition, and taking the wrong antibiotic delays the right treatment while encouraging resistance. Bring them to us for disposal and let somebody assess what you actually need.
This article is general information from the Dantrio Pharmacy team. It cannot take the place of advice from a pharmacist or doctor who knows your medical history. If you feel seriously unwell, seek medical help straight away.