If opioid involvement is suspected (heroin, fentanyl, morphine, strong painkillers), use naloxone nasal spray alongside resuscitation if available — sold over the counter in German pharmacies since 2024 as “Nyxoid”. Naloxone does not replace chest compressions, but it can reverse the depression of the respiratory centre.
Rescue breaths are optional for laypeople. Compressions without rescue breaths are better than nothing and easier for the untrained to perform correctly. If you can give rescue breaths: 30 compressions, then 2 breaths, alternating.
Work on a hard surface — a mattress or sofa absorbs the compression depth.