Below are the two best meta-analysis looking at steroids as pain control in pharyngitis.
Meta-analysis BMJ 2009:
Adult patients treated with corticosteroids were three times more likely to have complete resolution of pain at 24 hours and the number needed to treat was 3.7. Corticosteroids also increased the likelihood of complete resolution of pain at 48 hours, number needed to treat was 3.3. All effects were in addition to antibiotic use. The effects of corticosteroids on resolution of pain were most apparent in the initial 24 hours, which implies that a single dose of corticosteroids may be sufficient.
Meta-analysis Academic Emergency Medicine 2010:
When added to standard antibiotic therapy, corticosteroid treatment is associated with a 4.5-hour reduction in time to clinically meaningful pain relief. There is a minimal reduction in pain (0.9 points on a 10-point visual analog scale, where 1.3 points is a clinically meaningful change) occurring within 24 hours of treatment. These differences lack clinical relevance, and significant heterogeneity was identified in the pooled results. This review does not support the routine use of corticosteroids in the treatment of acute pharyngitis potentially caused by group A beta-hemolytic Streptococcus and physicians should weigh the risks and benefits of corticosteroids before instituting treatment..
These two meta-analysis differ in the criteria for data collection, abstraction, and pooling.
I was unable to find a decent study in which steroids were given for sore throat not treated with antibiotics. For now the evidence is inconclusive and each doctor will need to review the studies to make a decision on whether to use or not to use steroids. In the future hopefully a study is done for acute pharyngitis treated with steroids without antibiotics.
Hayward G, et al. Corticosteroids for pain relief in sore throat: systematic review and meta-analysis. BMJ. 2009 Aug 6;339:b2976. doi: 10.1136/bmj.b2976.
Wing A, et al. Effectiveness of corticosteroid treatment in acute pharyngitis: a systematic review of the literature. Acad Emerg Med. 2010 May;17(5):476-83.