A recent systematic review titled “Association between friendship quality and subjective wellbeing among adolescents: a systematic review” found across 43 quantitative studies that higher friendship quality is consistently associated with better wellbeing outcomes among adolescents including lower depression, less loneliness, higher life satisfaction, more happiness and greater self-esteem.

However, the review notes a key limitation: most of the evidence is cross-sectional (i.e., a snapshot). Longitudinal evidence (tracking changes over time) is much scarcer, which limits causal inference (does better friendship quality lead to better wellbeing, or vice-versa?).

For example, the association between friendship quality and loneliness is among the strongest and most consistent: adolescents reporting higher-quality friendships tend to report less loneliness.  The review also points to the need to consider mechanisms: how exactly does friendship quality operate? It suggests models like stress-buffering (good friendships help adolescents cope with stress), feelings of belongingness, self-worth, and peer support frameworks.

From our work and the broader literature:

• Quality matters more than quantity: It’s not just how many friends an adolescent has, but how positive and supportive those ties are.
• Friendship quality may serve as a protective factor against low mood, poor self-esteem, loneliness but the evidence is more robust cross-sectionally than over time.
• Adolescence is a critical developmental window: Friendships and peer relationships take on increasing importance in early to mid-adolescence for social and emotional outcomes.
• Interventions aiming to improve adolescent wellbeing should consider friendship-quality enhancement (e.g., conflict resolution, emotional support, trust) rather than only peer-behaviour change.

Implications for practice and future research:

1. Assessment and measurement: Interventions should include measures of friendship quality (not just number of friends or peer group size). Validated scales capturing trust, intimacy, conflict, companionship are important.
2. Intervention design: Interventions aimed at adolescent wellbeing might incorporate components to foster higher‐quality friendships. For example, buddy systems, peer-mentoring, social skills training, conflict resolution workshops, structured peer-group activities.
3. Focus on relational processes: Friendships are dynamic, relational systems. Understanding how adolescents form, maintain and experience friendships (including online/offline interplay) matters, particularly in a digital era.
4. Need for longitudinal research: To build stronger causal inference, more studies that follow adolescents over time are needed. For example: does improving friendship quality lead to improved wellbeing 6-12 months later?
5. Context and diversity: Friendship‐quality effects may vary by gender, culture, socio‐economic context, online vs offline friendships. Tailoring interventions to context is important.