So I gave up tea and coffee - indefinitely - because I was getting the black shakes (amongst other things) and being knackered at home after work is no fun. The first thing I noticed was 4 days of headaches in the afternoons. So I did a little research on the effects of caffeine withdrawal:
Coffee and Caffeine's Frequently Asked Questions: "What are the symptoms of caffeine withdrawal? Regular caffeine consumption reduces sensitivity to caffeine. When caffeine intake is reduced, the body becomes oversensitive to adenosine. In response to this [oversensitivity], blood pressure drops dramatically, causing an excess of blood in the head (though not necessarily on the brain), leading to a headache. This headache, well known among coffee drinkers, usually lasts from one to five days, and can be alleviated with analgesics such as aspirin. It is also alleviated with caffeine intake (in fact several analgesics contain caffeine dosages). Often, people who are reducing caffeine intake report being irritable, unable to work, nervous, restless, and feeling sleepy, as well as having a headache. In extreme cases, nausea and vomiting has also been reported."
Holy crap, anyone would think you were giving up crack!
So what about decaf - is that safe? It depends... sort of. It still contains caffeine (in small doses) and unless it's water filtered rather than using methylene chloride (which is a suspected carcinogenic) then maybe it's not so safe.
Strange which drugs are legal isn't it?