In plain words
That happiness born of the contact of senses with their objects, like nectar at first but like poison in the end, is remembered as rājasa.
Word for word
That which, from the contact of objects and senses, is like nectar at first, like poison in the end, that happiness is held rājasa.
विषयेन्द्रियसंयोगाद् यत् तदग्रेऽमृतोपमम्परिणामे विषमिव तत् सुखं राजसं स्मृतम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
विषयेन्द्रियसंयोगात् जायते यत् सुखम् तत् सुखम् अग्रे प्रथमक्षणे अमृतोपमम् अमृतसमम् , परिणामे विषमिव, बलवीर्यरूपप्रज्ञामेधाधनोत्साहहानिहेतुत्वात् अधर्मतज्जनितनरकादिहेतुत्वाच्च परिणामे तदुपभोगपरिणामान्ते विषमिव, तत् सुखं राजसं स्मृतम् ॥ ३८ ॥
In plain words
The pleasure born where the senses meet their objects is nectar at the beginning — in that first instant, nectar exactly. At the ripening it is poison. It costs you strength, vigour, beauty, insight, sharpness of mind, wealth and drive; it breeds adharma, and out of that adharma come hell and the rest. So at the ripening — at the far end, when the enjoying is spent and its result has arrived — it is poison. That pleasure is called rājasic.
Close to the Sanskrit
That pleasure which is born from the contact of sense-objects and the senses — that pleasure at the beginning, in the first moment, is like nectar, equal to nectar; at the ripening, like poison — because it is the cause of the loss of strength, vigour, beauty, insight, intelligence, wealth and drive, and because it is the cause of unrighteousness and of hell and the rest produced by that unrighteousness; therefore at the ripening, at the end of the transformation of the enjoyment of it, it is like poison. That pleasure is declared to be rājasic.