What's the best way to get rid of a headache?

Water, and sleep it off.
In my experience.

It pays to drink a glass of water before bed after an evening of alcohol.
- You sure? My wallet has always gotten smaller the next morning after drinking alcohol, whether or not I drank water before bed.
  
  /s
- Eat a steak before going to bed too, in that case. Meat works wonders for hangovers.

A Guillotine.

Paracetamol. Make sure you are well hydrated and a bit fed as well.

Ibuprofen and caffeine. After consuming, lay down and try to nap until the caffeine hits.

What kind of headache is it?

What do you mean?
- Like a migraine, sinus, pressure, or tension. Did anything seem to cause it? Does anything make it worse?

As other's have said, hydration. But that's only if you're dehydrated. There is a pressure point near the base of your thumb, a bit towards your pointer finger. You can look it up for more specifics. I find that hitting that pressure point helps about 20% of my headaches.

Lots of water, a quality meal and fresh air.

I typically go for a hike.

If you regularly consume caffeine and haven't recently: caffeine.

If you regularly consume nicotine but haven't recently: nicotine.

If you regularly consume any drug, really, but haven't recently: youre probably experiencing withdrawal; the most common side effects from withdrawal of most substances is a headache.

Caffeine, ibuprofen and a long walk combo helps me sometimes. I'm pissed they no longer sell ibuprofen with codeine here, that shit used to help me real fast.

Agree with the others here.

For future prevention, if you have money and since it's a tension headache - you might consider some corrective massage.

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find the cause (inflamation, etc)

Sleep

For me it's two 200 mg Ibuprofen.

Two 250 mg acetaminophen works, but not as well.

Aspirin kinda sucks for me in this role so I don't use it.

Sometimes, I've found that headaches can be caused by muscle tension or aches. I grind my teeth at night, for example, and if I forget to wear my mouthguard, I have headaches the next day. Often the tension is hard to spot until it's gone - I speculate that this is part of why sleeping tends to help with headaches.

If this is the cause, I've found that a strategy to identify and relax areas of tension is to work through an area and consciously tense the muscles, and then relax. It feels like turning something off and on again. Like if I've been doing computer work, my muscles around my eyes may be tired, and tensing the area for a few seconds and then releasing can help reduce that.