Bhagavad Gita Chapter 18, Verse 38

विषयेन्द्रियसंयोगाद्यत्तदग्रेऽमृतोपमम् | परिणामे विषमिव तत्सुखं राजसं स्मृतम् ||

viṣayendriya-saṁyogād yat tad agre 'mṛtopamam pariṇāme viṣam iva tat sukhaṁ rājasaṁ smṛtam

That happiness which arises from contact of senses with sense objects, which is like nectar in the beginning but like poison in the end, is remembered as rajasic.

Krishna explains rajasic happiness. 'Viṣayendriya-saṁyogād yat tad agre 'mṛtopamam'—that happiness which arises from contact of senses with sense objects (viṣaya-indriya-saṁyogāt), which is like nectar (amṛta-upamam) in the beginning (agre). 'Pariṇāme viṣam iva tat sukhaṁ rājasaṁ smṛtam'—but like poison (viṣam iva) in the end (pariṇāme), that happiness (tat sukham) is remembered (smṛtam) as rajasic (rājasam). This is rajasic happiness: pleasurable in the beginning, like nectar, but ultimately like poison, arising from contact of senses with sense objects. This is the middle kind of happiness: it feels good initially, but leads to suffering and creates more attachment. Unlike sattvic happiness (difficult initially but nectar-like in the end), rajasic happiness is pleasurable initially but becomes like poison. It's driven by rajas (passion), which creates attachment to sense pleasures. This is the path: recognizing that initial pleasure often leads to later suffering.