Afaik there was no sleeping meds/drugs found. I know it is a popular theory that the children were drugged but there is no evidence to support this that I am aware of.
I think I've posted about this before with less information, but people claim that the McCanns drugged the kids because they had Calpol with them, a readily available and extremely common children's paracetamol which is used by millions of parents for their childs pain relief, including
on flights for babies and children to this day. It doesn't cause drowsiness or put kids to sleep, it only acts on pain. In fact it is extremely common advice given by medical professionals to take things on holiday like Calpol and kids travel sickness tablets. They also still recommend in 2024 you take child antihistamines, which might cause a little drowsiness, which I mention due to the below.
This is all TOTAL speculation across SM and was never confirmed, but they MAY have had Calpol Night in the apartment. I don't think it was actually available on shelves until after May 2007 but can't find the source. It is same brand we all use today but contained both paracetamol and diphenhydramine hydrochloride, an antihistamine. Parents used it quite commonly after it's release to help children with discomfort at night if they had allergies, cough or a cold. A large number of antihistamines (including those used in Clarytin Kids, although a different type) MAY have a sedative effect in SOME patients but it's not guaranteed, just like any side effect of any medication, alongside a list of other side effects longer than your arms. Just like ANY medication does. It wasn't a guaranteed sedative and still isn't, and is not marketed as a child sedative.
Calpol Night was a common medication to give your children just like regular Calpol is today, and wasn't known to be a risk to children at the time so even if it was available at the time and the McCanns did give it to the kids with the extremely slim change that one side effect out of 50 or so would kick in, all they did was give their kids an easily acquired OTC medication. Calpol Night and other cough medicines for kids which also contained the antihistamine were marketed for 3 months plus until 2009 when legislation bumped limits to 2 years plus due to babies being negatively affected by it. It was withdrawn completely in the UK in 2010.
Edit: words.