I haven't had any headaches, and I am a frequent migraine suffer when my diet's upset (e.g. iron levels drop) so it's been good there. I was very tired the second and third day but feel fine now (8th). I think it's one of the cheapest TFR diets and for some it can be cheaper than eating, though I've found it more than my regular food bill. I'd order the taster pack from s&s, then I got mine off ebay, there's an official store but also others sell their's on there. I paid £80 for 3 weeks supply (84 packs). You can't pick and choose flavours (though they did substitute one of the bars I didn't like for another) but it's better value. It can get a bit dull though, because there's more of fewer flavours. So it's up to you which is more important, but definitely shop around. Good luck