Background. This report attempted to replicate and extend prior work examining social phobia (SP), co-morbid psychiatric illnesses, and the risk of suicidal ideation and suicide attempts incurred by their adolescent sufferers.

Methods. SP, alcohol dependence (ALD) and major depressive disorder (MDD) diagnoses, and suicide-related symptoms, were assessed in a population-based adolescent female twin sample. The differentiation of risks as a function of co-morbidity was explored. A trivariate model was fitted to estimate sharing of genetic and environmental vulnerability between SP and co-morbid disorders.

Results. The lifetime prevalence of SP was 16·3%. Significant risk for co-morbid MDD (OR = 3·2) and ALD (OR = 2·1) was observed. Strong evidence for shared genetic vulnerability between SP and MDD (respective heritabilities 28%, 45%; genetic r = 1·0) was observed with moderate support noted for similar sharing between SP and ALD (genetic r = 0·52, heritability for ALD 63%). SP with co-morbid MDD was associated with elevated risk for ALD and for suicide-related symptoms.

Conclusions. SP is a common illness often followed by co-morbid MDD and ALD. SP with co-morbid MDD predicts a substantially elevated risk of ALD and suicide-related symptoms, stressing the need for early SP detection.