The most important sentence on this page is the first one: do not give yourself another dose to make up for one you think went wrong. That is a prescribing decision, and the person who prescribed the medicine is the one who can make it. Contact them. The second most important thing is that most of what worries people here has never been studied, and knowing that is more useful than being handed a confident answer that nobody can support.
Subcutaneous: into the fat layer under the skin, rather than into muscle or a vein. It is the layer both medicines are registered to be given into (semaglutide, tirzepatide).
A drop appeared at the site
Common enough that people ask about it constantly, and unquantified.
No published figure exists for how much medicine a visible drop at the skin represents, or what it does to the dose actually delivered. We looked; it is not there. Any article telling you "a drop is only about 5% of the dose" has produced that number from nowhere.
So the practical answer is not a reassurance about the dose, because none is available. It is this: a visible drop is something to mention to your prescriber, and it is not a reason to inject again. The medicine is weekly, the next scheduled dose is a known quantity, and improvising a top-up introduces a risk that is real against a shortfall that is hypothetical.
You think it was a partial dose
Same evidence position, same answer, and this is the section the page exists for.
Nothing published tells you how to detect a partial dose after the fact, or what proportion of the intended amount you received. What is documented is the schedule the medicine is meant to follow, and the fact that changing it is a clinical decision.
The rule is the same whether you think you lost a little or most of it: the correction belongs to the prescriber. Getting in touch is not an overreaction, and it is a much smaller thing than a self-administered second dose.
The adjacent question — what to do when a dose is late or missed entirely — does have documented answers, and they differ between the two medicines. That is covered in what to do about a missed dose.
It went into muscle, or you think it did
What the labels support is narrow: these medicines are registered for subcutaneous injection, into the fat under the skin (semaglutide, tirzepatide).
Start here: tell the prescriber, and do not take a further dose in the meantime. That is the whole action, and for most people it will be the end of it — the medicine is weekly, so there is time to get an answer before the next scheduled dose.
Beyond the label's instruction, the specifics have not been studied. There is no published account of what follows an accidental intramuscular injection of these medicines, so someone telling you it is definitely fine and someone telling you it is dangerous are both going past the evidence. The person who prescribed it can weigh what is known against what you actually did, which is more than any page can do.
There was blood, or a bruise appeared straight away
A small amount of bleeding where a needle has gone through skin is not among the things either label flags.
Marks at the site are uncommon in general — 1.4% against 1% in people injecting placebo (label) — and bruises, marks and lumps covers what is ordinary, what is not, and the short list that warrants a call.
The wrong site
This is the most common version of "I did it wrong", and it usually comes from the two medicines having different site lists.
Semaglutide's label names the abdomen, thigh and upper arm. Tirzepatide's names the abdomen and thigh, and states the back of the upper arm is for another person to administer rather than for injecting yourself (semaglutide, tirzepatide). So a site that is correct for one medicine is not automatically correct for the other, and general advice picked up online is a common source of the mix-up.
Check the leaflet that came with your own pen, which is written for exactly what you were dispensed. The site lists and the clearance from the navel are also set out in injection sites, storage and travel. If you have used a site that is not on your leaflet's list, raise it — do not repeat it, and do not compensate for it.
What is usually not worth worrying about
Worth saying, because this page could otherwise leave the impression that everything is a problem.
A small bead of blood, a brief sting, a faint mark that fades within the day, or being unsure whether you held the pen quite long enough — these are the things people ask about most and they are the least likely to matter. The medicine is dosed weekly, which means the schedule has more tolerance built into it than a daily medicine would.
The line worth holding is not "never worry". It is that the worry gets directed at a person who can answer it rather than resolved by guessing, and that no amount of uncertainty about a dose justifies giving yourself another one. Everything on this page reduces to that.
What to tell the prescriber
Being specific saves a round of questions. Useful to have ready:
- What happened, in one sentence
- When it happened, and whether it was a scheduled dose
- Which site you used
- What you saw — a drop, a bruise, bleeding, a mark
- Whether you have done anything since, including whether you have taken any further dose
That last point matters most. If you have already given yourself a second dose, say so plainly and immediately. It changes what they need to do, and there is nothing to be gained by leaving it out.
If you have not started treatment and this page found you while you were deciding, your first GLP-1 injection covers the shape of a first dose. You can also check your eligibility and speak to a doctor about whether this is suitable for you.
Common questions
Some liquid leaked out — did I lose the dose?
Nobody has published how much a visible drop represents or what it does to the dose delivered. What is clear is the safe response: do not give yourself more to compensate, and contact the person who prescribed it.
Should I inject again if I think I only got part of the dose?
No, not on your own judgement. Repeating or topping up a dose is a prescribing decision, and the person who prescribed it is the one who can make it.
What if it went into muscle?
Both medicines are registered to be given subcutaneously — into the fat layer under the skin rather than into muscle (semaglutide, tirzepatide). What actually follows an accidental intramuscular injection of these medicines has not been studied, so anyone answering confidently is guessing. Tell the prescriber.
There was a spot of blood. Is that a problem?
A small amount of bleeding at a skin puncture is not among the things the labels flag. Marks at the site are uncommon overall, at 1.4% against 1% on placebo (label).
I used the wrong site. Does it matter?
The two medicines have different site lists, which is where most of this confusion starts (semaglutide, tirzepatide). Check the leaflet for your own pen, and raise it with the prescriber if you are unsure.