Are there any similar drugs to alcohol?

Depends on the drug. If it is opiates then it does what it says it will do and increase the effect. But if it is Ambien then you need to be careful or you might keep sleeping if it is your first try then small doses till your body can meet you. I'm a over 10 year drug addict (recovering) so please be careful.

That depends on the drug. Many drugs have serious negative consequences when combined with alcohol intake. Sometimes the effect is just decreasing the effectiveness of the drug, but it can be more serious. As the previous answerer already noted, combining opiates with alcohol can increase the effect of the drug - with negative effects up to and including death.

As with all drugs, if you are one who indulges in an alcoholic drink now and then, you need to talk with your doctor and/or pharmacist about potential interactions of any drugs with the alcohol.