I’ve seen lots of posts saying you shouldn’t be started on 25mcg of Levo as an adult and that it should generally be 50mcg as a starting dose, except for certain circumstances.
Can starting on 25mcg make things worse instead of better? If so, what are some of the symptoms that could arise?
It appears that a very small dose can reduce your own thyroid hormone product by more than the amount you are taking.
Maybe you don't reduce by quite as much as you take, but it does seem to mean that small doses can only increase thyroid hormone levels by a very small amount.
Any symptoms would at worst be a slight increase in those you'd expect from hypothyroidism - and probably already have.
25mcg is a starting dose and also if someone is very frail.
50mcg is a starting dose with a blood test and 25mcg increase every six weeks until you feel much improved and symptoms relieved.
Your symptoms will just be several of the following:-
thyroiduk.org.uk/tuk/about_...
Do you do the following when getting a blood test?
i.e.
Get the earliest possible blood test. Fasting (you can drink water) and allow a gap of 24 hours between your last dose of levo and the test and take afterwards.
This gives you the best results but you should have an increase every six weeks until symptoms resolve. Many doctors think that 'somewhere' in the tsh range is fine (up to 5) but the aim is a TSH of 1 or lower.
GP should also check B12, Vit D, iron, ferritin and folate. Everything has to be optimal.
When I started out everyone started on 25 mcg so I'm supposing a high percentage had no problems with that so was moved up to 50. As long as your doctor has told you to return in 6 weeks for more bloods to check levels again and if you need more( most likely will) he increases your dose and this is repeated until you are one the correct dose for you. But you mentioned feeling worse, a few do but improve with the next dose increase but can you explain a bit more about your symptoms as other things may be the problem. All thyroid tablets have fillers in them to bulk them up and to keep them stable so may be that's where the problem is but is generally more like an allergic reaction.
I actually feel a lot better since taking the tablets than before treatment.
The only thing that’s worse is my lack of period and now very long cycle. I last had a period on Feb 25th. Currently on cycle day 45. I’ve never skipped a month before!
That's not unusual and should settle down when you get further down the line.
On 25mcg levothyroxine 
levothyroxine 25mcg in brown medicine bottles 
How long to feel benefit of 25mcg levothyroxine increase?
First Stopped meds and then started reduced to 25mcg
Endocrinologist not raising sister’s dose above 25mcg?!
