As a part of my PhD comparing orthotics and corticosteroid injections for plantar fasciitis, I have just published a review of the effectiveness of orthotics. The article has been published in the British Journal of Sports Medicine, and found that orthotics are effective at reducing pain, but not immediately. We found that they were most effective approximately 2-3 months after starting to use orthotics.
Clinically, this may indicate that it is important to combine orthotics with another treatment that is effective at reducing pain in the short term, such as shockwave therapy.
A short video summary of the findings is below:
Whittaker et al. (2017). Foot orthoses for plantar heel pain: a systematic review and meta-analysis. Br J Sports Med. doi: http://bjsm.bmj.com/content/early/2017/09/21/bjsports-2016-097355.